2 * Copyright 2014 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #include "folly/Bits.h"
19 #include "folly/CpuId.h"
20 #include "folly/Portability.h"
22 // None of this is necessary if we're compiling for a target that supports
28 int popcount_builtin(unsigned int x) {
29 return __builtin_popcount(x);
32 int popcountll_builtin(unsigned long long x) {
33 return __builtin_popcountll(x);
36 #if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
38 // Strictly speaking, these versions of popcount are usable without ifunc
39 // support. However, we would have to check, via CpuId, if the processor
40 // implements the popcnt instruction first, which is what we use ifunc for.
41 int popcount_inst(unsigned int x) {
43 asm ("popcntl %1, %0" : "=r" (n) : "r" (x));
47 int popcountll_inst(unsigned long long x) {
49 asm ("popcntq %1, %0" : "=r" (n) : "r" (x));
53 typedef decltype(popcount_builtin) Type_popcount;
54 typedef decltype(popcountll_builtin) Type_popcountll;
56 // This function is called on startup to resolve folly::detail::popcount
57 extern "C" Type_popcount* folly_popcount_ifunc() {
58 return folly::CpuId().popcnt() ? popcount_inst : popcount_builtin;
61 // This function is called on startup to resolve folly::detail::popcountll
62 extern "C" Type_popcountll* folly_popcountll_ifunc() {
63 return folly::CpuId().popcnt() ? popcountll_inst : popcountll_builtin;
66 #endif // FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
73 // Call folly_popcount_ifunc on startup to resolve to either popcount_inst
74 // or popcount_builtin
75 int popcount(unsigned int x)
76 #if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
77 __attribute__((ifunc("folly_popcount_ifunc")));
79 { return popcount_builtin(x); }
82 // Call folly_popcount_ifunc on startup to resolve to either popcountll_inst
83 // or popcountll_builtin
84 int popcountll(unsigned long long x)
85 #if FOLLY_HAVE_IFUNC && !defined(FOLLY_SANITIZE_ADDRESS)
86 __attribute__((ifunc("folly_popcountll_ifunc")));
88 { return popcountll_builtin(x); }
94 #endif /* !__POPCNT__ */